1. Field of the Invention
The present invention relates to a positive displacement piston pump. More specifically, the present invention relates to a piston pump of the type having a drive shaft that is driven by a rotary motor and a piston which is axially movable within a cylinder and is connected with a piston guide shaft. The drive shaft and the piston guide shaft are rotatably coupled to each other and are axially movable with respect to each other. The drive shaft and the piston guide shaft are also coaxially aligned with respect to each other. The piston guide shaft is connected to a guide element, which is guided in a guide way.
2. Description of the Related Art
Positive displacement piston pumps, per se, are well known. For example, U.S. Pat. No. 3,168,872 describes a positive displacement piston pump where, in a first embodiment, the drive shaft and the piston guide shaft are disposed at an angle with respect to each other. A crank housing is provided on the drive shaft and includes a ball receptor with a ball being disposed therein. The ball forms an end of a crank which in turn is connected to the piston guide shaft. By changing the angle between the drive shaft and the piston guide shaft, a change in the length of the stroke of the piston can be obtained. In a second embodiment, the drive shaft and the piston guide shaft are aligned coaxially with respect to each other. A crank is provided on the piston guide shaft. A ball is provided at the end of the crank, and the ball is guided in a guide way which in turn is disposed in a pivotal housing. By pivoting the housing, the length of the stroke of the piston can be adjusted to vary the feed volume of the pump.
U.S. Pat. No. 5,158,441 describes another positive displacement piston pump in which the angle between the guide shaft and the piston guide shaft can vary. By changing the angle, the stroke length of the piston is changed. The drive connection of the piston drive shaft itself is achieved by a crank that is connected to the drive shaft and is guided by its head into a coupling. The coupling is connected with the piston drive shaft.
In both of the above examples of positive displacement piston pumps, it is difficult to precisely adjust the length of the stroke of the piston and, thus, the feed volume of the pump. Even in the applications where the angle between the drive shaft and the piston guide shaft is not adjustable, large tolerances prevail so that inaccuracies can only be minimized (i.e., not eliminated) with great difficulty by machining the individual parts with high precision.